Engines, including diesel engines, gasoline engines, natural gas engines, and other engines known in the art, exhaust a complex mixture of air pollutants. The air pollutants may be composed of gaseous and solid material, which can include particulate matter. Due to increased attention on the environment, exhaust emission standards have become more stringent and the amount of particulate matter emitted from an engine may be regulated depending on the type of engine, size of engine, and/or class of engine.
A method used by engine manufacturers to reduce the amount of particulate matter emitted to the environment includes removing the particulate matter from the exhaust flow of an engine with a device called a particulate filter. A particulate filter is designed to trap particulate matter and typically consists of a wire mesh or ceramic honeycomb filtration medium. Although efficient at removing particulate matter from an exhaust flow, the use of the particulate filter for extended periods of time can cause the particulate matter to build up in the filtration medium, thereby reducing the functionality of the filter and subsequent engine performance. The collected particulate matter can be removed from the filtration medium through a process called regeneration. To initiate regeneration of the filtration medium, the temperature of the particulate matter entrained within the filtration medium is elevated to a combustion threshold, at which the particulate matter is burned away in the presence of oxygen or NO2.
Regeneration of a filtration medium may be implemented passively, relying on heat contained with the exhaust flow that was generated solely during engine combustion. Alternatively, regeneration of a particulate filter may be implemented actively, relying upon an auxiliary heat source, such as a fuel-fired burner, to elevate the temperature of the exhaust flow to a temperature capable of combusting particulate matter. Regeneration strategies that rely solely on passive regeneration may be ineffective at maintaining sufficient temperatures to ensure regeneration. Whereas, regeneration strategies based solely on active regeneration may inefficiently heat particulate matter when regeneration of the particulate filter is not necessary, thereby increasing the cost and complexity of the regeneration system.
One example of an exhaust emission control device implementing passive and active regeneration strategies is described in U.S. Pat. No. 6,725,653 (the '653 patent) to Brown et al. The '653 patent discloses a system including an engine emitting exhaust into a particulate filter. The '653 patent also includes a controller to regulate operation of a heat source. The controller receives data from a temperature sensor and a pressure sensor to determine when the amount of particulate matter within the filter exceeds a threshold amount. When the amount of detected particulate matter exceeds the threshold amount or after a defined period of time, the controller signals the heat source to operate in an active regeneration mode. The heat source operates in either a full or partial exhaust flow via a bypass value to vary the amount of exhaust flow allowed to pass through the heat source. The bypass valve can preserve fuel supplied to the heat source by limiting the amount of exhaust flow that is heated.
Although prior art systems may alleviate some of the problems associated with filter regeneration, there is a need for a more efficient and less complex filter regeneration system. The prior art systems incorporate complex components and complex control that increase system cost and maintenance. The disclosed exhaust treatment system is directed to overcoming problems associated with the prior art systems.